Many electrical components, such as integrated circuits, require connection to a voltage source separate and distinct from any incoming signals. Without such an independent voltage source, many of these components will not function properly. Many such components also have other inputs to receive stable voltage signals that may be used for reference purposes. For instance, some microprocessors (such as the INTEL 8097) have a V.sub.cc port for connection to a regulated 5 volt source, and a V.sub.ref port for receiving a stable reference voltage signal of 5 volts. The 8097 provides the latter input to ensure the availability of an accuate reference signal (V.sub.ref) that can be compared with other inputs as received by the 8097. For instance, through this comparison process, the 8097 can accurately measure incoming sensor signals as may be received at the above noted inputs.
These needs could be accomodated by simply providing three separate regulated voltage sources; one for the V.sub.cc input, one for the V.sub.ref input, and one to supply voltage for the sensor inputs (a V.sub.sensor supply). Unfortunately, accuracy requirements often forbid such independance as between the V.sub.sensor source and the V.sub.ref source. If V.sub.ref and V.sub.sensor differ from one another by any appreciable amount, the microprocessor may not be able to correctly interpret the incoming sensor signals. Therefore, V.sub.ref and V.sub.sensor are often interelated to some extent to alleviate this source of inaccuracy.
With some components, however, such as the above mentioned 8097, this interelationship raises additional problems. For example, the 8097 may be disabled if the V.sub.ref signal differs greatly from the V.sub.cc signal. If the V.sub.ref signal tracks the V.sub.sensor signal, and the V.sub.sensor signal deviates from an accepted norm, the V.sub.ref signal will also deviate, causing a differential to grow between V.sub.ref and V.sub.cc. This differential can, as noted above, disable the part.
There therefore exists a need for a voltage tracking control device that can be utilized with a multiple voltage source system such that a V.sub.ref signal can be provided that will track a V.sub.sensor voltage under ordinary operating conditions, but that will track the V.sub.cc signal under abnormal operating conditions to ensure that a microprocessor or other component as used in conjunction therewith will not be unnecessarily damaged during fault scenarios.